We go through a lot of art supplies at our house. I've always loved them, so having kids just gives me an excuse to buy fun things. Liquid watercolours were new to me. I had read about them on Artful Parent, but it was a while before I made the investment. We have several paints already. Would liquid watercolours be different enough to be worth the price? If you are trying to stockpile an extremely cool art cabinet, then I say the answer is "yes!"
The vibrancy and colour intensity of the liquid watercolours far surpasses the watercolour paint sets we typically use. More than that, the liquid form opens up interesting possibilities for exploration and additional development of fine motor skills. I purchased a variety of liquid watercolours from Discount School Supply and several different sizes of droppers to drip or squirt the colour onto thick watercolour paper or (even better) coffee filters.
Sometimes, we paint the paper with tap water first. Sometimes, we leave the paper dry. Often, we'll do a wet and a dry page side by side, so the kids can witness the different effects. We have cut the coffee filters into shapes and made garlands. The colour saturation and blending on a coffee filter is incredibly fun to watch (and keep!).
By far, the most requested use of our liquid watercolours is salt painting. We use cut-up cereal boxes instead of paper, because they have to handle a lot of moisture. Squeeze white school glue in squiggles or designs until satisfied. Then, cover the entire work with table salt (I buy a big box just for this craft and reuse again and again) the same way you would with glitter. Shake off the excess. Then, drip liquid watercolours into the salt and watch it spread. We have never succeeded in saving one of these great works, but the process is more the point.